There has been recent data developed which indicates that the crushed stone, rock and gravel fills under concrete highways and asphalted shoulders have not performed as expected to rapidly disperse rainwater away from the highway and its base, but allow the accumulation of some water under concrete pavements, particularly at the edges thereof, resulting in earlier breakdown of the pavement than expected. As a result of these studies, it has been proposed to provide more adequate drainage, a type of drain which will receive rainwater shortly after it falls upon the pavement and highway and conducting the same rapidly away from the highways and its base materials to lateral ditches where the runoff will not affect the pavement. Some studies show that pavement life, such as utilized throughout the country on the interstate highway system, may have a prolonged life of 40 years compared to its present estimated 20-year life. Such adequate drainage can be provided by drainage tubing installed closely adjacent the lateral edges of the concrete slab to receive water which invariably tends to flow over the pavement and enter a seam between the concrete and the asphalt shoulder or berm. Such drainage tiling can be provided with laterals every 300 or so feet to exit collected water into side ditches. It has been found that during a rainstorm, 4 inch drainage tile, so installed, will flow an apparently solid stream of water into the ditches indicating rapid collection and conduction of rainwater away from under paving.
The cost of installing drainage tubing beside highways by conventionally known methods is excessively high. Where exceedingly long corrugated wall-perforated drainage tubing is installed immediately behind a chain trencher, such as disclosed in our copending application Ser. No. 728,556, filed Oct. 1, 1976, now U.S. Pat. No. 4,028,902, the ability to adequately compact sand over the tile free of loose soil may be accomplished. Other installations, however, require the mechanical joining of finite lengths, such as 10 foot long lengths, or "Orangeburg" pipe, which generally requires an installation at some distance rearward of the trenching operation to be followed by a sand fill and compaction over the so laid drainage tiling. In such instances, it is important that the trench left by the trenching machinery be free of loose dirt and that the ground surface on either side of the trench also be free of loose dirt or soil so that the drainage tubing may be installed and the sand compaction be placed thereover, free of loose soil.
It is to solve the problems of trenching with a high-speed chain trencher so as to form a trench beside a highway, substantially lowering the cost of so doing, while depositing loose soil away from the trench, leaving the trench in proper condition to receive drainage tiling and properly compacted sand fill thereover. Bearing in mind that vehicles which leave a highway slab and pass onto the shoulder will pass over the trench location, it is important that the trench be properly backfilled with the sand fill thereover properly compacted to sustain the weight of such vehicles. Heretofore, high-speed trenchers have not been thought to be operable to clean trench operation due to the throwing of removed soil so randomly about the excavation site.